The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Study shows not all fat is bad

Fat cells found under the skin, known as adipocytes, produce proteins that protect humans against bacteria and other pathogens, a study published in the journal Science shows.

Dr Richard Gallo, chief of dermatology at University of California San Diego School of Medicine, who led the research, says the protective role of these fat cells was unknown until now.

Researchers focused on adipocytes producing anti-microbial peptides, which help the body to fight bacteria and other pathogen agents.

"It was thought that once the skin barrier was broken, it was entirely the responsibility of circulating (white) blood cells like neutrophils and macrophages to protect us from getting sepsis," Gallo said.

However, it takes time for white cells to reach the wound area and while they are preparing to launch their action, skin cells provide protection.

"We now show that the fat stem cells are responsible for protecting us," Gallo said.

"That was totally unexpected. It was not known that adipocytes could produce antimicrobials, let alone that they make almost as much as a neutrophil."

The study describes the body's complex defensive processes against microbial infection, involving different types of cells that intervene in different levels.

However, the research also shows that an excess of fat cells may lead to the development of autoimmune or inflammatory diseases like lupus, psoriasis or rosacea.